Methods of forming ruthenium film by changing process conditions during chemical vapor deposition and ruthenium films formed thereby

ABSTRACT

A ruthenium (Ru) film is formed on a substrate as part of a two-stage methodology. During the first stage, the Ru film is formed on the substrate in a manner in which the Ru nucleation rate is greater than the Ru growth rate. During the second stage, the Ru film is formed on the substrate in a manner in which the Ru growth rate is greater than the Ru nucleation rate.

RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.1999-61337, filed Dec. 23, 1999 and Korean Patent Application No.2000-12056, filed Mar. 10, 2000, the disclosures of which are herebyincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to chemical vapor deposition(CVD) and, more particularly, to forming ruthenium films by CVD andruthenium films and integrated circuit devices formed thereby.

BACKGROUND OF THE INVENTION

Noble metals, such as ruthenium (Ru), platinum (Pt), iridium (Ir) andosmium (Os), have traditionally been used infrequently in semiconductorintegrated circuits. Recently, however, these noble metals and/or theoxidized substances thereof have been studied for potential use as alower or upper electrode of a capacitor. This is because the desiredelectrical characteristics for a capacitor may not be attainable byusing polysilicon, which is commonly used as an electrode material whena material, such as Ta₂O₅, BST ((Ba, Sr)TiO₃) or PZT((Pb, Zr)TiO₃), thathas a high dielectric constant is used as a dielectric film. Because Ruhas a generally good leakage current characteristic and may be etchedmore easily than Pt, attention has been focused on the use of Ru film asthe electrode of a capacitor.

Traditionally, sputtering methods have been used to form Ru films. Inaccordance with conventional sputtering methods, a Ru film may bedensely formed and a generally good surface morphology may be achieved,thereby obtaining a Ru film having a generally good leakage currentcharacteristic and a generally good resistance characteristic. Onedisadvantage to conventional sputtering methods, however, is that the Rufilms formed thereby may provide poor step coverage. As a result,sputtering methods may be less desirable when forming an electrodehaving a three-dimensional shape, such as a cylinder shape or a finshape.

CVD has been proposed for forming Ru films because films formed by CVDgenerally have better step coverage than those formed by sputteringmethods. Specifically, in conventional CVD methods, Ru is deposited on asubstrate or an interlayer dielectric layer using a vaporized Ru sourcegas and a reactant gas (i.e., a catalyzer) so that generally good stepcoverage can be achieved. Unfortunately, the surface morphology of a Rufilm formed by CVD is typically worse than that of a Ru film formed byconventional sputtering methods. As a result, it may be difficult toobtain desired leakage current and resistance characteristic usingconventional CVD methods. Consequently, there exists a need for improvedCVD methods for forming Ru film.

SUMMARY OF THE INVENTION

According to embodiments of the present invention, a ruthenium (Ru) filmis formed on a substrate as part of a two-stage methodology. During thefirst stage, the Ru film is formed on the substrate in a manner in whichthe Ru nucleation rate is greater than the Ru growth rate. During thesecond stage, the Ru film is formed on the substrate in a manner inwhich the Ru growth rate is greater than the Ru nucleation rate. Whenthe Ru film is formed in a manner such that the nucleation rate isgreater than the growth rate, the density and uniformity of the Rugrains in the film may be enhanced, which may provide a smooth surfacemorphology. When the Ru film is formed in a manner such that the growthrate is greater than the nucleation rate, the Ru grains in the film maygrow substantially uniformly in various directions, but the nuclei maynot be densely formed. As a result, the sheet resistance of the Ru filmmay be reduced. Moreover, the smooth surface morphology of the Ru filmformed during the initial deposition stage may advantageously facilitatethe formation of a continuous Ru film in the second deposition stage.Thus, a Ru film formed in accordance with embodiments of the presentinvention may be viewed as comprising two portions: a first portionhaving relatively densely formed nuclei having a relatively smoothsurface morphology and a second portion having relatively sparselyformed nuclei. The relatively smooth surface morphology of the Ru filmformed during the first deposition stage may facilitate the formation ofa continuous Ru film during the second deposition stage and therelatively sparsely formed nuclei of the Ru film formed during thesecond deposition stage may provide for improved electricalcharacteristics in the form of reduced sheet resistance.

In further embodiments of the present invention, a Ru film is formed ona substrate by chemical vapor deposition (CVD) using a Ru source gas andoxygen as a reactant gas. During the formation of the ruthenium film onthe substrate by CVD, one or more of the following process conditionsare changed: the CVD chamber pressure, the oxygen gas flow rate, and thesubstrate temperature. For example, in particular embodiments of thepresent invention, the CVD chamber pressure may be decreased, the oxygengas flow rate may be decreased, and/or the substrate temperature may beincreased during the deposition of the Ru film. While the CVD chamberpressure and the oxygen gas flow rate are relatively high and thesubstrate temperature is relatively low, the Ru film may be formed withrelatively dense nuclei so that a relatively smooth surface morphologymay be achieved. Conversely, while the CVD chamber pressure and/or theoxygen gas flow rate are relatively low and/or the substrate temperatureis relatively high, the Ru film may be formed with relatively sparselyformed nuclei for reduced sheet resistance. Thus, by changing any or allof the three process conditions corresponding to the CVD chamberpressure, the oxygen gas flow rate, and the substrate temperature, thephysical and electrical characteristics of the Ru film may be varied.

In still further embodiments of the present invention, a two-stepmethodology may be used to form a Ru film. For example, in a first step,a Ru film may be formed on a substrate by CVD using a Ru source gas andoxygen as a reactant gas at a first CVD chamber pressure and firstoxygen gas flow rate. In a second step, the Ru film is formed on thesubstrate by CVD using the Ru source gas and oxygen as a reactant gas ata second CVD chamber pressure and second oxygen gas flow rate.Importantly, however, either or both of the second CVD chamber pressureand second oxygen flow rate are less than the first CVD chamber pressureand first oxygen flow rate, respectively.

In particular embodiments of the present invention, the first CVDchamber pressure is in a range from about 10 Torr to 50 Torr, the secondCVD chamber pressure is in a range from about 0.05 Torr to 10 Torr, thefirst oxygen flow rate is in a range from about 500 sccm to 2000 sccm,and the second oxygen flow rate is in a range from about 10 sccm to 300sccm.

In still further embodiments of the present invention, the substratetemperature is in a range from about 250° C. to 450° C. during bothsteps of the two-step methodology for forming the Ru film. In otherembodiments of the present invention, however, the substrate temperatureis about 10° C. to 30° C. higher when performing the second step of thetwo-step methodology than it is when performing the first step of thetwo-step methodology.

In yet further embodiments of the present invention, the Ru film may beheat treated at about 250° C. to 450° C. in an atmosphere comprisingoxygen or ozone after the first step of the two-step methodology and/orafter completing both steps of the two-step methodology.

In other embodiments of the present invention, integrated circuitdevices, such as capacitors, may be formed by forming a lower and/or anupper electrode as a Ru film as described in the foregoing.

Thus, in summary, the present invention may be used to form Ru films bychanging at least one process condition during the CVD methodology. As aresult, Ru films having improved continuity and reduced sheet resistancemay be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of the present invention will be more readily understoodfrom the following detailed description of specific embodiments thereofwhen read in conjunction with the accompanying drawings, in which:

FIGS. 1-3 are photographs taken by a scanning electronic microscope(SEM) of the surfaces of ruthenium (Ru) films formed by chemical vapordeposition (CVD) under various process conditions;

FIG. 4 is a graph that illustrates the morphological distribution of Rufilms, which are formed by CVD at different chamber pressures andsubstrate temperatures;

FIG. 5 is a graph that illustrates the morphological distribution of Rufilms, which are formed by CVD at different chamber pressures and oxygenflow rates;

FIG. 6 is a flowchart that illustrates methods of forming rutheniumfilms by changing process conditions during CVD in accordance withembodiments of the present invention;

FIG. 7 is a photograph taken by a SEM of a surface of a Ru film formedin accordance with embodiments of the present invention;

FIG. 8 is a graph that illustrates the results of an X-ray diffractionanalysis of Ru films formed by CVD under various process conditions;

FIG. 9 is a graph that illustrates the results of an X-ray diffractionanalysis of Ru films formed by sputtering;

FIG. 10 is a graph that illustrates the results of an X-ray diffractionanalysis of a Ru oxide film formed by CVD;

FIG. 11 is a graph that illustrates the results of an oxygenconcentration analysis in Ru films formed by CVD under various processconditions and by sputtering by using a secondary ion mass spectrometer;

FIG. 12 is a graph that illustrates the measured sheet resistance in Rufilms formed by CVD under various process conditions;

FIG. 13 is a graph that illustrates the reflectances of Ru films formedby CVD under various process conditions and by sputtering;

FIGS. 14A and 14B are photographs taken by a SEM of the surface and asection of a Ru film formed by CVD in accordance with embodiments of thepresent invention; and

FIG. 15 is a sectional view of a capacitor having an electrode thatcomprises an Ru film formed by CVD in accordance with embodiments of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular forms disclosed, but on the contrary, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims. In the drawings, the thickness of layers and regions areexaggerated for clarity. Like numbers refer to like elements throughoutthe description of the figures. It will also be understood that when anelement, such as a layer, region, or substrate, is referred to as being“on” another element, it can be directly on the other element orintervening elements may also be present. Conversely, when an element isindicated as being “directly on” another element, there are nointervening elements present.

When forming a ruthenium (Ru) film by chemical vapor deposition (CVD), asubstrate is typically loaded into the CVD chamber and a Ru source gasand a reactant gas are supplied to the chamber. Examples of a suitableRu source gas include Ru(C₂H₅C₅H₄)₂ (Bis(EthylCyclopentadienyl)Ruthenium (hereinafter Ru(EtCp)₂)), Ru(CH₃CH₂CH₂CH₂C(O)CH+C(O—)CH₃)₃(Tris(2, 4-OctaneDionato) Ruthenium), which is liquid at roomtemperature, Ru(C₁₁H₁₉O₂)₃ (Tris(DiPivaloylMetanate) Ruthenium), andRu(C₅H₅)₂ (Bis(Cyclopentadienyl) Ruthenium), which is solid at roomtemperature. A solid source may be melted and vaporized to generate thesource gas. A liquid source may be directly vaporized to generate thesource gas. Oxygen gas may be used as a reactant gas (i.e, a catalyzer)for separating Ru atoms from the Ru source gas and depositing them on asubstrate. During deposition, an inert gas such as argon or nitrogen,may be used as a carrier gas for smoothly supplying the Ru source gas orreactant gas and as a purge gas for purging the deposition chamber.

Typically, a Ru film is chemical vapor deposited for several minutes ata chamber pressure of several Torr through dozens of Torr, with anoxygen flow rate of dozens of sccm (standard cubic centimeter perminute) through several thousand sccm, and at a substrate temperature of250°-450° C. In conventional CVD methods, a Ru film is typicallydeposited under constant process conditions. In accordance withembodiments of the present invention, however, Ru films are formed bychanging the process conditions during the CVD procedure.

Before describing methods of forming Ru films in accordance withembodiments of the present invention, it may be helpful to examine thecharacteristics of Ru films formed by CVD methods under fixed processconditions. In general, when a Ru film is formed by CVD, the surfacemorphology, which may influence electrical characteristics, such asleakage current and resistance, may vary depending on the processconditions. Under certain process conditions, a Ru film may be formedsuch that the Ru grains grow in a disorderly fashion so as to form“needles” (hereinafter referred to as a needle-shape Ru film) as shownin FIG. 1. Under other process conditions, a Ru film may be formed suchthat the Ru grains grow in a disorderly fashion so as to form “plates”(hereinafter referred to as a plate-shape Ru film) as shown in FIG. 2.Under still other process conditions, a Ru film may be formed such thatthe Ru grains grow in a sparse fashion so as to form bulky “rocks”(hereinafter referred to as a rock-shape Ru film) as shown in FIG. 3.

The CVD conditions for forming the Ru films shown in FIGS. 1 through 3are as follows:

Ru film of FIG. 1—Substrate temperature: 350° C., Pressure: 19 Torr,Oxygen flow rate: 750 sccm;

Ru film of FIG. 2—Substrate temperature: 350° C., Pressure: 1 Torr,Oxygen flow rate: 750 sccm; and

Ru film of FIG. 3—Substrate temperature: 350° C., Pressure: 1 Torr,Oxygen flow rate: 150 sccm.

Further experimentation in depositing Ru films under various CVD processconditions has revealed the following tendencies: A needle-shape Rufilm, as shown in FIG. 1, may generally be obtained at a low substratetemperature, at a high chamber pressure, and with a high oxygen flowrate; a rock-shape Ru film, as shown in FIG. 3, may generally beobtained at a high substrate temperature, at a low chamber pressure, andwith a low oxygen flow rate; and a plate-shape Ru film, as shown in FIG.2, may generally be obtained under process conditions that are betweenthe conditions associated with the needle-shape Ru film and therock-shape Ru film. As shown in FIGS. 4 and 5, the morphology of a Rufilm varies depending on the substrate temperature, the chamberpressure, and the oxygen flow rate. Typical characteristics of needle,plate, and rock-shape Ru films based on morphology are discussedhereafter.

A needle-shape Ru film results from grains growing rapidly in onedirection and slowly in other directions. In a needle-shape Ru film,nuclei are densely formed, but the surface morphology is generally poor(i.e., the surface is rough). As a result, the sheet resistance isgenerally high and leakage current may increase when the Ru film isused, for example, as the lower electrode of a capacitor. A rock-shapeRu film is characterized by grains that grow uniformly in multipledirections, but the nuclei are generally not densely formed.Accordingly, when a thick rock-shape Ru film is deposited, the surfacemorphology may be better than that of a needle-shape Ru film, which mayresult in a lower sheet resistance. When a rock-shape Ru film is thinlydeposited, however, an underlayer may be exposed due to the sparselyformed nuclei. Consequently, it may be difficult to deposit a thinrock-shape Ru film. The characteristics of a plate-shape Ru filmgenerally lie between the characteristics of the needle-shape Ru filmand the rock-shape Ru film.

When a Ru film is used as a capacitor electrode having athree-dimensional shape, such as a cylinder shape, in a semiconductordevice having a high integration density, it is generally desirable touniformly deposit a thin film (e.g., a thickness of less than 1000 Å)that has a good step coverage and excellent electrical characteristics.Accordingly, in view of the foregoing discussion, it may be difficult touse a needle-shape Ru film or a rock-shape Ru film as a capacitorelectrode. Although a plate-shape Ru film, which is a compromise betweenthe needle-shape Ru film and the rock-shape Ru film, may be used, everydesired characteristic may not be satisfied.

In accordance with embodiments of the present invention, Ru films havingboth good continuity and good surface morphology may be obtained bychanging one or more CVD process conditions during the Ru depositionprocedure. Referring now to FIG. 6, in an initial deposition phase orstage, Ru is deposited at block S110 under conditions that facilitate anucleation rate that is faster than the growth rate (i.e., underconditions that produce a needle-shape film) to form dense and uniformRu grains. At block S130, Ru is deposited under conditions thatfacilitate a growth rate that is faster than a nucleation rate (i.e.,under conditions that produce a rock-shape film) to uniformly grow theRu grains. Note that in the second deposition stage, the Ru film that isformed is not a conventional rock-shaped film as described hereinabove,but is instead a particular shaped Ru film that is formed based on thecondition that an underlying layer thereof is an Ru film formed underconditions that facilitate a nucleation rate that is faster than thegrowth rate.

In particular embodiments of the present invention, during the initialdeposition phase or stage, Ru is deposited for about 5 seconds to 5minutes while a chamber pressure is maintained at about 10-50 Torr(preferably 20-40 Torr) and an oxygen flow rate is maintained at about500-2000 sccm (preferably 1000-1500 sccm). During a second or laterdeposition phase or stage, Ru is deposited until a Ru film of a desiredthickness is obtained while the chamber pressure is maintained at about0.05-10 Torr (preferably 0.1-3 Torr) and the oxygen flow rate ismaintained at about 10-300 sccm (preferably 50-150 sccm). For example,when vaporized Ru(EtCp)₂ is used as a Ru source gas, a 100% undilutedsolution of Ru(EtCp)₂ may be supplied to the chamber at a flow rate of0.01-0.3 ccm. Alternatively, Ru(EtCp)₂ may be mixed with a solvent suchas tetrahydrofuran (THF) and supplied to the chamber at a flow rate ofmore than 0.01-0.3 ccm. A substrate temperature may be maintainedsubstantially constant throughout the CVD procedure at about 250°-450°C. (preferably 300°-350° C.). Alternatively, the substrate temperaturemay be lower during the initial deposition phase or stage and higherduring the second or later deposition phase or stage. When the substratetemperature is changed during the CVD procedure, the difference betweenthe temperatures in the two phases or stages is preferably 10°-30° C. Inaccordance with embodiments of the present invention, the substratetemperature may be changed discretely (e.g., in one or more steps) orcontinuously. Similarly, the chamber pressure and oxygen flow rate mayalso be changed discretely or continuously.

As described above, at least two CVD process conditions, such as thechamber pressure and the oxygen flow rate, are simultaneously changedduring the CVD procedure. In accordance with further embodiments of thepresent invention, only one among the three CVD process conditions ofchamber pressure, oxygen flow rate, and substrate temperature may bechanged to adjust the relative difference between nucleation rate andgrowth rate for the Ru film. By changing one of the aforementioned CVDprocess conditions, the combined conditions may be converted fromconditions that facilitate the formation of a needle-shape Ru film intoconditions that facilitate the formation of a rock-shape Ru film andvice versa. In other words, conditions under which a needle-shape Rufilm is formed may be established in an initial phase or stage and thenconditions under which a rock-shape Ru film is formed may be establishedin a later phase or stage by changing only one of the three CVD processconditions of chamber pressure, oxygen flow rate, and substratetemperature and fixing the remaining two conditions as shown in FIGS. 4and 5. The Ru film that is formed in the second deposition stage is nota conventional rock-shaped film as described hereinabove, but is insteada particular shaped Ru film that is formed based on the condition thatan underlying layer thereof is an Ru film formed under conditions thatfacilitate a nucleation rate that is faster than the growth rate. From aproductivity standpoint, it is generally preferable to change either orboth of the chamber pressure and the oxygen flow rate rather than thesubstrate temperature because it generally takes longer to obtain thedesired temperature.

FIG. 7 is a photograph taken by a scanning electron microscope (SEM) ofa surface of a Ru film formed in accordance with embodiments of thepresent invention. The Ru film of FIG. 7 is obtained by depositing Ru ina two-step CVD process with changes in the chamber pressure and theoxygen flow rate. In a first step, Ru is deposited for about one minutewhile the chamber pressure is maintained at about 19 Torr and the oxygenflow rate is maintained at about 750 sccm. In a second step, Ru isdeposited for about one minute while the chamber pressure is maintainedat about 5 Torr and the oxygen flow rate is maintained at about 100sccm. During the two steps, the substrate temperature is maintained atabout 350° C.

Referring to FIG. 7, the resulting Ru film is similar to the rock-shapeRu film of FIG. 3, but its surface is generally smoother and its grainsare more densely formed as compared to the Ru film of FIG. 3 (note thatthe photograph of FIG. 7 has been enlarged about 1.5 times theenlargement applied in FIGS. 1-3). Thus, according to embodiments of thepresent invention, a thin seed layer of Ru film characterized by densenucleation may be formed in the first step. In the second step, the Rufilm may grow substantially uniformly in multiple directions centeringaround seeds on the thin seed layer so that Ru film grows into arock-shape or columnar shape, which is generally more dense than therock-shape Ru film of FIG. 3. The thin seed layer portion of the Ru filmmay provide a relatively smooth surface morphology, which may facilitatethe formation of a continuous Ru film during the second deposition step.In addition, the second portion of the Ru film may provide improvedelectrical characteristics in the form of reduced sheet resistance.

The characteristics of Ru films formed in accordance with embodiments ofthe present invention in which process conditions are changed during theCVD will be compared with the characteristics of conventional needle,plate, and rock-shape Ru films. FIG. 8 is a graph that illustratesresults of an X-ray diffraction analysis of Ru films formed by CVD undervarious environmental conditions. As shown in FIG. 8, in the case of aneedle-shape Ru film sample, the overall peak intensity is generally lowand the grains do not grow in a (002) direction, which is generally thedensest surface of a Ru film having a hexagonal close-packed structure.In the case of a rock-shape Ru film sample, the particles grow in the(002) direction generally more than in the other samples. A Ru filmsample formed in a two-step CVD deposition according to embodiments ofthe present invention shows similar characteristics to those of a sampleplate-shape Ru film. It appears, therefore, that the growth pattern ofRu particles is substantially the same in both a plate-shape Ru film andan Ru film formed through a two-step CVD process, according toembodiments of the present invention, in which the deposition conditionsare selected so as to cause the nucleation rate to be faster than thegrowth rate during an initial deposition stage and the growth rate isfaster than the nucleation rate during a second deposition stage.Inasmuch as dense nucleation may be achieved in the initial step, themorphology of the Ru film sample formed according to embodiments of thepresent invention is generally good.

Referring now to FIG. 9, a graph is shown that illustrates the resultsof an X-ray diffraction analysis of Ru films formed by sputtering. Amain peak in the (101) direction does not appear as it does in the Rufilms formed by CVD as shown in FIG. 8. A peak does appear in the (002)direction, which is towards the densest surface, particularly at hightemperature (e.g., 400° C.). Based on these data, it appears that the Rugrains grow in a direction that is characterized by high density due tothe nature of sputtering at high temperature (i.e., physical collisionsbetween atoms and the substrate).

FIG. 10 is a graph that illustrates the results of an X-ray diffractionanalysis of a ruthenium oxide (RuO₂) film formed by CVD. The positionsof the peaks of the ruthenium oxide film shown in FIG. 10 are clearlydifferent from the positions of the peaks of the Ru film, which isformed according to embodiments of the present invention, and is shownin FIG. 8. Thus, the Ru films formed by CVD according to embodiments ofthe present invention do not have the phase of a ruthenium oxide filmeven though they contain oxygen as an impurity.

FIG. 11 is a graph that illustrates the results of an oxygenconcentration analysis in Ru films formed on a silicon oxide film bysputtering and by CVD under various process conditions, includingchanging process conditions, by using a secondary ion mass spectrometer(SIMS). In FIG. 11, the horizontal axis denotes the depth of a Ru film,and the vertical axis denotes the counted number of secondary ionsseparated from a Ru film. Reference numeral 100 denotes a needle-shapeRu film, reference numeral 110 denotes a rock-shape Ru film, referencenumeral 120 denotes a plate-shape Ru film, reference numeral 130 denotesa Ru film formed by a two-step CVD methodology according to embodimentsof the present invention, and reference numeral 140 denotes a Ru filmdeposited by sputtering.

Referring now to FIG. 11, because the needle-shape Ru film 100 isdeposited at a high chamber pressure and with a large oxygen flow rate,its oxygen concentration profile is highest and is generally constant.For the rock-shape Ru film 110 and the plate-shape Ru film 120, theoxygen concentration profile slowly and continuously increases as depthincreases. For the Ru film 130 formed by the two-step CVD according toembodiments of the present invention, the oxygen concentration profileis low and generally constant down to a predetermined depth from thesurface at which point it rapidly increases. This is because, asdescribed above, the oxygen flow rate is larger during the first step ofthe deposition and smaller during the second step of the depositionaccording to embodiments of the present invention. For the Ru film 140formed by a sputtering method, an oxygen concentration profile is lowand generally constant down to a predetermined depth from the surface atwhich point it slowly increases.

It is assumed, however, that the Ru film formed by sputtering has a lowand substantially constant oxygen concentration profile due to the smallamount of oxygen included in the atmosphere within the sputteringchamber. It appears, therefore, that the increase in the oxygenconcentration profile of the Ru film 140 of FIG. 11 once a predetermineddepth is reached may be caused by oxygen contained in a silicon oxidefilm, which is an underlayer of the Ru film, being separated andcounted. Accordingly, it appears that the increase in the oxygenconcentration profile of the Ru film 140 may be caused by an error inthe SIMS analysis. Taking this SIMS analysis error into account, theoxygen concentration profile of the Ru film 130, which is formed by atwo-step CVD methodology in accordance with embodiments of the presentinvention, may slope more sharply at the dashed line 150, substantiallyapproximating a step function. The dashed line 150 indicates theboundary between a Ru film portion deposited in a first step and a Rufilm portion deposited in a second step during a two-step depositionaccording to embodiments of the present invention.

FIG. 12 is a graph that illustrates the measured sheet resistance in Rufilms formed by CVD under various process conditions. More specifically,the reference numerals denote Ru films having different sheetresistances based on different oxygen flow rates. Reference numeral 210denotes a Ru film formed with an oxygen flow rate of 150 sccm. Referencenumeral 220 denotes a Ru film formed with an oxygen flow rate of 350sccm. Reference numeral 230 denotes a Ru film formed with an oxygen flowrate of 750 sccm. Reference numeral 240 denotes a Ru film formed with anoxygen flow rate of 1500 sccm. Reference numeral 250 denotes a bulk Rufilm. As shown in FIG. 12 and discussed hereinabove, the sheetresistance of a needle-shape Ru film (formed at a high chamber pressureand with a large oxygen flow rate) is high and the sheet resistance of arock-shape Ru film (formed at a low chamber pressure and with a smalloxygen flow rate) is low. Although a Ru film formed by changing processconditions during CVD is not illustrated in FIG. 12, the sheetresistance of a Ru film so formed, according to embodiments of thepresent invention described hereinabove, has been measured to be lessthan or equal to 20 μΩ•cm.

FIG. 13 is a graph that illustrates reflectances of Ru films formed byCVD under various process conditions and by sputtering. Reflectance isgenerally indicative of surface morphology (i.e., the roughness of thesurface). In FIG. 13, the reflectance of each Ru film is expressed as arelative value to the reflectance of a silicon surface, which is set to100. As illustrated in FIG. 13, the surface of a needle-shape Ru film isroughest, the surface of a Ru film deposited by sputtering is smoothest,and the smoothness of the surface of a Ru film that is formed by CVD intwo steps, according embodiments of the present invention, is similar tothat of the Ru film formed by sputtering.

The step coverage of Ru films formed by changing process conditionsduring CVD in accordance with embodiments of the present invention hasalso been experimentally measured. Specifically, a Ru film has beenformed on a silicon oxide film having a trench formed therein at a depthof about 1 μm using a two-step CVD process according to embodiments ofthe present invention. A Ru film has also been formed on a tantalumoxide (Ta₂O₅) film having a trench formed therein at a depth of about 1μm using a two-step CVD process according to embodiments of the presentinvention. The step coverage of the two aforementioned Ru films wasmeasured and was found to be about 70-90%, which is a generally goodresult. It was found that better step coverage may be obtained when thetemperature in the second CVD step is higher than the temperature in thefirst CVD step.

FIGS. 14A and 14B are photographs taken by a SEM of the surface and asection of a Ru film, respectively, which was formed on a tantalum oxidefilm under the following conditions in accordance with embodiments ofthe present invention:

Chamber pressure: 19 Torr (first step); 1 Torr (second step)

Oxygen flow rate: 750 sccm (first step); 100 sccm (second step)

Substrate temperature: 315° C. (first step); 330° C. (second step)

Deposition time: 1 minute (first step); 3 minutes (second step)

As illustrated in FIGS. 14A and 14B, a Ru film formed in accordance withembodiments of the present invention may be uniformly deposited.

A Ru film formed by CVD typically includes small amounts of carbon,which is contained in the ruthenium source gas, and oxygen, which isprovided as a reactant gas, as impurities. Impurities may deterioratethe electrical characteristics of a Ru film. For example, carbongenerally increases the resistance of a Ru film. Therefore, it ispreferable that the amount of impurities contained in a Ru film is keptlow.

In accordance with further embodiments of the present invention, heattreatment may be performed in an oxygen or ozone atmosphere to improvethe electrical characteristics of a Ru film. When depositing a Ru filmin two steps as described hereinabove with respect to blocks S110 orS130 of FIG. 6, heat treatment is performed at a pressure of about 1-100Torr and a temperature of about 240°-450° C. in an oxygen or ozoneatmosphere, in-situ or ex-situ, after the first deposition step at blockS120 and/or after the second deposition step at block S140. The heattreatment may improve the electrical characteristics of the Ru film byremoving the carbon impurities contained therein. An inert gas, such asargon or nitrogen, may be supplied during the heat treatment.

FIG. 15 is a sectional view of a capacitor having an electrode thatcomprises an Ru film formed by CVD in accordance with embodiments of thepresent invention. Referring now to FIG. 15, a lower electrode contactplug 310 is formed in a substrate or interlayer dielectric layer 300.Next, an interlayer dielectric layer 320 having an opening that exposesthe lower electrode contact plug 310 is formed.

Subsequently, a Ru film 350 for a lower electrode is formed on theentire surface of the resultant structure by changing process conditionsduring CVD in accordance with embodiments of the present inventiondiscussed hereinabove. For example, in an initial step, a Ru filmportion 330 is deposited under conditions that cause the nucleation rateto be faster than the growth rate (i.e., conditions that facilitate arelatively smooth surface morphology). In a succeeding step, a Ru filmportion 340 is deposited under conditions that cause the growth rate tobe faster than the nucleation rate (i.e., conditions that facilitateuniform growth in multiple directions) until the Ru film 350 reaches adesired thickness. The entire surface of the resultant structure maythen be chemical mechanical polished, for example, to remove the Ru film340 deposited on the top surface of the interlayer dielectric layer 320and to expose the interlayer dielectric layer 320, thereby separatingthe lower electrode 350 from adjacent lower electrodes.

Thereafter, a dielectric film 360 is formed on the entire surface of theresultant structure. Although not shown, the dielectric film 360 may beformed after removing the interlayer dielectric layer 320 and exposingthe outer wall of the cylinder-type lower electrode 350. This canenlarge the effective area of the electrode. The dielectric film 360preferably comprises a ferroelectric material, such as BST or PZT, or amaterial with a high dielectric constant, such as Ta₂O₅.

Next, an upper electrode 370 is formed on the entire surface of thedielectric film 360. Like the lower electrode 350, the upper electrode370 may comprise a Ru film and may be formed by changing processconditions during CVD in accordance with embodiments of the presentinvention described hereinabove. Besides Ru, the upper electrode 370 maycomprise impurity doped polysilicon, another noble metal, such asplatinum, iridium, or the oxidized material thereof, or anotherconductive metal compound, such as TiN or TiSiN. In further embodimentsof the present invention, the lower electrode 350 may comprise aconductive material other than a Ru film formed in accordance with thepresent invention, and the upper electrode 370 may comprise a Ru filmformed by changing process conditions during CVD.

In addition, when forming the lower electrode 350 and/or the upperelectrode 370 by a two-step CVD methodology in accordance withembodiments of the present invention discussed hereinabove, heattreatment may be performed in an oxygen or ozone atmosphere between thefirst and second deposition steps of the Ru film or after the seconddeposition step. Moreover, when the dielectric film 360 comprises aferroelectric material or a material with a high dielectric constant,heat treatment for crystallization of the dielectric film 360 materialmay be performed after forming the dielectric film 360 or after formingthe upper electrode 370.

Although a cylinder type lower electrode has been described herein forpurposes of illustration, the lower electrode of the capacitor may beany type, such as a simple stack type or a pin type, when the lowerand/or upper electrode comprises a Ru film that is formed by changingprocess conditions during a CVD process in accordance with embodimentsof the present invention.

Although particular process conditions are recited herein in describingmethods of forming a Ru film according to embodiments of the presentinvention, it will be understood that specific numerical values for thevarious CVD conditions (i.e., CVD chamber pressure, oxygen flow rate,and substrate temperature) may vary depending on equipment or thefabrication environment. For example, an oxygen flow rate may go beyondan exemplified range depending on the size of the deposition chamber. Itis understood that the skilled artisan can select proper numericalvalues for the CVD process conditions based on a particular environmentwithout departing from the spirit of the present invention, in whichfirst Ru film deposition conditions are selected to allow a nucleationrate to be faster than a growth rate and second Ru film depositionconditions are selected to allow the growth rate to be faster than thenucleation rate.

From the foregoing it can readily be seen that the present invention maybe used to form a Ru film by changing process conditions during CVD soas to cause the nucleation rate to be faster than the growth rate in aninitial stage and under conditions that cause the growth rate to befaster than the nucleation rate in a later stage. Advantageously, a Rufilm having a combination of good step coverage, surface morphology, andelectrical characteristics may be obtained.

In addition, the present invention may be used to form lower and/orupper electrodes out of a Ru film for a capacitor having athree-dimensional shape, such as a cylinder shape or a pin shape, so asto provide improved step coverage, which is typically not provided byconventional sputtering methodologies. Moreover, the electricalcharacteristics of the Ru film electrodes formed by changing processconditions during CVD are generally comparable to the Ru film electrodesformed by conventional sputtering techniques.

Another potential drawback with conventional technology is that adielectric film comprising a ferroelectric material or a material with ahigh dielectric constant may deteriorate due to hydrogen passing throughan upper electrode during the process of forming an intermetaldielectric layer, a metal wire, and a passivation layer in a hydrogenatmosphere after the formation of a capacitor. Advantageously, it hasbeen found that deterioration of a dielectric film due to penetration ofhydrogen may be reduced when a Ru film that is formed by changingprocess conditions during CVD is used as an upper electrode.

In concluding the detailed description, it should be noted that manyvariations and modifications can be made to the preferred embodimentswithout substantially departing from the principles of the presentinvention. All such variations and modifications are intended to beincluded herein within the scope of the present invention, as set forthin the following claims.

We claim:
 1. A method of forming a ruthenium film, comprising the stepsof: reacting a ruthenium source gas and oxygen at a first pressure andat a first oxygen gas flow rate to deposit ruthenium on a substrate; andreacting the ruthenium source gas and oxygen at a second pressure and ata second oxygen gas flow rate to deposit ruthenium on the substrate,wherein at least one of the second pressure and the second oxygen gasflow rate is less than the first pressure and the first oxygen gas flowrate, respectively.
 2. A method as recited in claim 1, wherein the firstpressure is in a range from about 10 Torr to 50 Torr.
 3. A method asrecited in claim 1, wherein the second pressure is in a range from about0.05 Torr to 10 Torr.
 4. A method as recited in claim 1, wherein thefirst oxygen gas flow rate is in a range from about 500 sccm to 2000sccm.
 5. A method as recited in claim 1, wherein the second oxygen gasflow rate is in a range from about 10 sccm to 300 sccm.
 6. A method asrecited in claim 1, wherein a substrate temperature is in a range fromabout 250° C. to 450° C.
 7. A method as recited in claim 6, wherein thesubstrate temperature is about 10° C. to about 30° C. higher whenperforming the step of reacting the ruthenium source gas and oxygen atthe second pressure and at the second oxygen gas flow rate than thesubstrate temperature is when performing the step of reacting theruthenium source gas and oxygen at the first pressure and at the firstoxygen gas flow rate.
 8. A method as recited in claim 1, furthercomprising the step of: heating the deposited ruthenium at a temperaturein a range from about 250° C. to 450° C. in an atmosphere that comprisesa gas selected from the group consisting of oxygen and ozone after thestep of reacting the ruthenium source gas and oxygen at the firstpressure and at the first oxygen gas flow rate.
 9. A method as recitedin claim 8, wherein the step of heating the deposited ruthenium at thetemperature in the range from about 250° C. to 450° C. in the atmospherethat comprises the gas selected from the group consisting of oxygen andozone comprises the step of: heating the deposited ruthenium at thetemperature in the range from about 250° C. to 450° C. in the atmospherethat comprises the gas selected from the group consisting of oxygen andozone at a CVD chamber pressure in a range from about 1 to 100 Torr. 10.A method as recited in claim 1, further comprising the step of: heatingthe deposited ruthenium at a temperature in a range from about 250° C.to 450° C. in an atmosphere that comprises a gas selected from the groupconsisting of oxygen and ozone after the steps of reacting the rutheniumsource gas and oxygen at the first pressure and at the first oxygen gasflow rate and reacting the ruthenium source gas and oxygen at the secondpressure and at the second oxygen gas flow rate.
 11. A method as recitedin claim 10, wherein the step of heating the deposited ruthenium at thetemperature in the range from about 250° C. to 450° C. in the atmospherethat comprises the gas selected from the group consisting of oxygen andozone comprises the step of: heating the deposited ruthenium at thetemperature in the range from about 250° C. to 450° C. in the atmospherethat comprises the gas selected from the group consisting of oxygen andozone at a CVD chamber pressure in a range from about 1 to 100 Torr. 12.A method as recited in claim 1, wherein the ruthenium source gas isselected from the group consisting of vaporized Ru(C₂H₅C₅H₄)₂(Bis(EthylCyclopentadienyl) Ruthenium), Ru(C₁₁H₁₀O₂)₃(Tris(DiPivaloylMetanate) Ruthenium), Ru(C₅H₅)₂ (Bis(Cyclopentadienyl)Ruthenium), and Ru(CH₃CH₂CH₂CH₂CH₃C₅H₃)₃ (Tris(2,4-OctaneDionato)Ruthenium).
 13. A method of forming a ruthenium film, comprising thesteps of: reacting a ruthenium source gas and oxygen to depositruthenium on a substrate; and changing at least one of a pressure, anoxygen gas flow rate, and a substrate temperature during the step ofreacting the ruthenium source gas and oxygen.
 14. A method as recited inclaim 13, wherein the step of changing at least one of the pressure, theoxygen gas flow rate, and the substrate temperature comprises the stepof: decreasing the pressure from a range of about 10 to 50 Torr to arange of about 0.05 to 10 Torr.
 15. A method as recited in claim 13,wherein the step of changing at least one of the pressure, the oxygengas flow rate, and the substrate temperature comprises the step of:decreasing the oxygen gas flow rate from a range of about 500 to 2000sccm to a range of about 10 to 300 sccm.
 16. A method as recited inclaim 13, wherein the step of changing at least one of the pressure, theoxygen gas flow rate, and the substrate temperature comprises the stepof: increasing the substrate temperature by an amount ranging from about10° C. to 30° C. while maintaining the substrate temperature in a rangefrom about 250° C. to 450° C.
 17. A method as recited in claim 13,wherein the ruthenium source gas is selected from the group consistingof vaporized Ru(C₂H₅C₅H₄)₂ (Bis(EthylCyclopentadienyl)Ruthenium),Ru(C₁₁H₁₀O₂)₃ (Tris(DiPivaloylMetanate) Ruthenium), Ru(C₅H₅)₂(Bis(Cyclopentadienyl) Ruthenium), and Ru(CH₃CH₂CH₂CH₂CH₃C₅H₃)₃(Tris(2,4-OctaneDionato) Ruthenium).
 18. A method of forming a rutheniumfilm, comprising the steps of: forming the ruthenium film on a substratesuch that the ruthenium nucleation rate is greater than the rutheniumgrowth rate; and forming the ruthenium film on the substrate such thatthe ruthenium growth rate is greater than the ruthenium nucleation rate.19. A method as recited in claim 18, further comprising the step of:heating the ruthenium film at a temperature in a range from about 250°C. to 450° C. in an atmosphere that comprises a gas selected from thegroup consisting of oxygen and ozone after the step of forming theruthenium film on the substrate such that the ruthenium nucleation rateis greater than the ruthenium growth rate.
 20. A method as recited inclaim 19, wherein the step of heating the ruthenium film at thetemperature in the range from about 250° C. to 450° C. in the atmospherethat comprises the gas selected from the group consisting of oxygen andozone comprises the step of: heating the ruthenium film at thetemperature in the range from about 250° C. to 450° C. in the atmospherethat comprises the gas selected from the group consisting of oxygen andozone at a pressure in a range from about 1 to 100 Torr.
 21. A method asrecited in claim 18, further comprising the step of: heating theruthenium film at a temperature in a range from about 250° C. to 450° C.in an atmosphere that comprises a gas selected from the group consistingof oxygen and ozone after the steps of forming the ruthenium film on thesubstrate such that the ruthenium nucleation rate is greater than theruthenium growth rate and forming the ruthenium film on the substratesuch that the ruthenium growth rate is greater than the rutheniumnucleation rate.
 22. A method as recited in claim 21, wherein the stepof heating the ruthenium film at the temperature in the range from about250° C. to 450° C. in the atmosphere that comprises the gas selectedfrom the group consisting of oxygen and ozone comprises the step of:heating the ruthenium film at the temperature in the range from about250° C. to 450° C. in the atmosphere that comprises the gas selectedfrom the group consisting of oxygen and ozone at a pressure in a rangefrom about 1 to 100 Torr.
 23. A method of forming an integrated circuitdevice, comprising the steps of: forming a lower electrode on asubstrate; forming a dielectric layer on the lower electrode; andforming an upper electrode on the dielectric layer; wherein at least oneof the lower electrode and the upper electrode comprises a rutheniumfilm formed by the following steps: forming the ruthenium film bychemical vapor deposition (CVD) using a ruthenium source gas and oxygenas a reactant gas at a first CVD chamber pressure and at a first oxygengas flow rate; and forming the ruthenium film by CVD using the rutheniumsource gas and oxygen as the reactant gas at a second CVD chamberpressure and at a second oxygen gas flow rate, wherein at least one ofthe second CVD chamber pressure and the second oxygen gas flow rate isless than the first CVD chamber pressure and the first oxygen gas flowrate, respectively.
 24. A method of forming an integrated circuitdevice, comprising the steps of: forming a lower electrode on asubstrate; forming a dielectric layer on the lower electrode; andforming an upper electrode on the dielectric layer; wherein at least oneof the lower electrode and the upper electrode comprises a rutheniumfilm formed by the following steps: forming the ruthenium film bychemical vapor deposition (CVD) using a ruthenium source gas and oxygenas a reactant gas; and changing at least one of a CVD chamber pressure,an oxygen gas flow rate, and the substrate temperature during the stepof forming the ruthenium film.
 25. A method of forming an integratedcircuit device, comprising the steps of: forming a lower electrode on asubstrate; forming a dielectric layer on the lower electrode; andforming an upper electrode on the dielectric layer; wherein at least oneof the lower electrode and the upper electrode comprises a rutheniumfilm formed by the following steps: forming the ruthenium film on asubstrate such that the ruthenium nucleation rate is greater than theruthenium growth rate; and forming the ruthenium film on the substratesuch that the ruthenium growth rate is greater than the rutheniumnucleation rate.